This invention relates generally to an apparatus and method for forming flat cut carton blanks into erected cartons, and, more particularly, to an apparatus and method for debowing the erected carton side panels during the forming operation.
Apparatus are known for forming flat cut carton blanks into erected cartons. The carton blanks are generally of rectangular configuration having a bottom panel and opposing side and end panels connected therewith along fold lines. Locking tabs are provided on the end panels for engagement with slits provided on the side panels during the forming operation. Locking retention between the tabs and slits serves to maintain the cartons in erected condition for subsequent filling and/or lidding operations.
Known carton forming apparatus typically include a feeder mechanism for depositing a carton blank onto a die. A forming head, or plunger, of rectangular configuration corresponding to the erected carton size, then engages the carton bottom panel to force the blank in a descending forming stroke through the die. The die includes forming guides engaging the carton sides and end panels during passage of the forming head through the die. In this manner, the carton side and end panels gradually bend along their fold lines into upright position relative to the carton bottom panel, in engagement with corresponding end and side walls of the forming head. The die also includes stripper fingers to force the locking tabs into the slits.
During further operation, the forming head descends completely through the die, where spring-loaded fingers, such as the type disclosed in U.S. Pat. No. 2,997,930 to Pierce (owned by the assignee of the present invention) are positioned to project slightly into the path of the forming head. As the forming head descends below the fingers into an end-of-stroke position, the biased fingers engage the upper edges of the carton side panels. Thereafter, the forming head ascends to receive the next in-line carton blank. However, since the carton is now positively arrested by the fingers, the erected carton is stripped from the forming head and dropped onto a suitable conveyor positioned below.
Due to the natural flexural strength or bending memory of the carton side panels, the erected panels sometimes tend to be outwardly bowed after passing through the die, as is shown in FIG. 2a of the drawing. Consequently, difficulties are encountered in applying and sealing lids on the erected cartons, resulting in increased production time. Furthermore, in view of the outwardly bowed condition of the side panels, the cartons exhibit less than ideal product retention properties. Also, a carton with bowed sides is unsightly and hinders the sales appeal of product. In the past, where the problem is acute, the only solution is to perform a separate debowing operation on the carton. This, of course, adds considerable expense and slows the carton forming operation.
An improved method and apparatus for debowing the carton side panels during the carton forming process is disclosed in U.S. patent application entitled Apparatus and Method for Forming and Debowing Cartons Ser. No. 329,878, of Collura et al., filed Dec. 11, 1981, commonly assigned with the present invention. In the Collura et al. application, presser fingers pivotally secured to the forming guides are biased into the forming head path with spring means. During descending movement of the forming head, the spring means produces a force sufficient to urge the presser fingers against the fold lines and the carton side panels, thereby creasing the fold lines and overbreaking the panels into cutout openings in the forming head side walls.
While this method and apparatus for debowing the side panels is believed superior to prior methods, due to the stiffness characteristics of certain paperboard, some carton blanks tend to resist the simple spring-loaded pressing action of the presser fingers. Such resistance prevents full debowing action from occurring. Thus, with some carton blanks stronger and more controlled creasing action is needed to assure the necessary overbreaking action of the side panels.